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Fred P. Hain

North Carolina State University

Integrated pest management (IPM) in a forest ecosystem is the process of managing a forest with all available tools so that potentially destructive organisms, such as insects and diseases, are maintain at a level that is below an economic or damage threshold.  These tools are used in conjunction with forest management practices that are designed to meet the overall goals of the forest manager.  The tools of IPM include pest thresholds (economic or damage), preventive cultural practices, monitoring, mechanical controls, biological controls and chemical controls (including the use of pheromones).  As a rule-of-thumb, forest management practices that encourage good growth produce pest resistant stands.  Typically, pest problems arise in stands that are under stress.  Many stress factors, but not all, are caused by poor management practices that can be alleviated.

Pest Thresholds

 
Forest ecosystems consist of a variety of components, all of which are critical to the forest’s long-term sustainable health.  Insects, fungi and other microorganisms play and important role in forest stability, succession and productivity by contributing to the degradation of dead and dying trees, nutrient recycling of decaying organic matter, creating openings for regeneration, providing a food source for other organisms, pollination (certain insects), and predation or parasitism of potentially harmful pests.  Thus it is important for forest managers to recognize that forest management practices can have an impact on the other components of the ecosystem that could be detrimental to long-term forest stability. 

The goal of forest management should be to maintain all components of the system in a balance that enhances the likelihood of long-term sustainability.  Even certain pests, such as bark beetles, that have the potential of being highly destructive, can be beneficial to the forest ecosystem at low population levels by removing stressed trees.  The objectives of forest management should not be to eradicate potential pest species, but to keep them in check (the one exception to this would be an invasive or exotic pest that has not coevolved with the system). Therefore, the concept of a “pest threshold” refers to the level at which an organisms inflicts significant damage to the forest ecosystem resulting in economic loss.

Preventive Cultural Practices
 

In forestry, IPM was practiced before the concept was defined.  The concept of IPM evolved as a result of the environmental movement that demanded less use of broad-spectrum pesticides in agricultural and urban settings.  Because of costs and logistical problems the use of pesticides in many forest systems has had limited use historically.  The exceptions to this would be intensively managed stands such as seed orchards, Christmas tree plantations, nurseries, and newly planted stands.  Also eradication efforts of an invasive pest will sometimes rely heavily on pesticides.  Generally, however, foresters have had to rely on preventive cultural practices to keep pest populations in check.  Cultural practices include thinning, weed control, site selection, and occasional fertilization.  These are practices that enhance the growth and health of the remaining trees and, as a consequence, make them less susceptible to pest attack.  In other words, good silvicultural practices usually means good pest management. 

Monitoring

When establishing an IPM program, monitoring is an essential first step.  In agriculture, the concept is simple. Monitoring or scouting is done to prevent the prophylactic application of pesticides; do not apply pesticides if not needed.  In many cases, an IPM program does not go beyond an intensive monitoring program.  In forestry, monitoring is essential since pesticide applications are usually cost-prohibitive. 

Monitoring can take on many forms: scouting and sampling, pheromone trapping, tree baits, and aerial surveillance. Sometimes combinations of methods are used such as aerial surveillance to detect dead trees and ground checking to determine the cause of mortality.  In some cases more than one life stage of a pest is required before control measures are taken.  For example, pheromone trapping may detect a large concentration of adult male moths in a given location.  This is followed by a ground survey for the egg stage to verify that mating and reproduction has taken place. Regular observations, good record keeping, and a thorough knowledge of the pest’s life cycle are the foundation for an IPM program.

 
Mechanical Controls

Mechanical controls in forestry generally mean salvage or the removal of infested trees to prevent the spread of a pest.  If the cut trees can be utilized, the control operation may be cost-effective.  In some instances, the infested trees may be too few or too remote for a cost-effective operation.  Cut-and-leave or cut-and-treat are options that are frequently employed for bark beetle control.  The infested trees, along with a buffer, are simply cut down and left or treated by debarking, applying a pesticide, or burning.   It is assumed that any surviving beetles will disperse and not create additional infestations.  On high-value trees, mechanical control could include simple handpicking, erecting insect or pathogen barriers, or sticky traps.

 
Biological Controls
 

Biological control is the reliance on natural enemies, such as parasites, predators, or diseases, to keep a pest population in check.  There are three types of biological control: importation, conservation, and augmentation.  Importation is sometimes called “classical biological control.” Normally it is utilized against exotic pests where natural enemies from the pest’s homeland are introduced into the newly infested region.  It is assumed that once the natural enemy is established it will be self-maintained.  Care must be taken to avoid natural enemies that will have a significant impact on non-target species. 

Conservation biological control includes the identification and remediation of negative influences that suppress natural enemies already in the system, and the enhancement of habitat for natural enemies.  For example, providing alternative food sources for natural enemies, such as pollen and nectar, by encouraging selected flowering plants. Using more selective pesticides that have minimal impact on natural enemies is another approach. 

Augmentation biological control is the release of enemy populations, which were artificially reared, for pest suppression.  It is used when natural enemies are missing, too scarce, or slow to arrive. There are two strategies for augmentation releases.  The first is “inoculative,” where the released organisms and the progeny of the released organisms accomplish control of the pest.  The second is “inundative,” where the released organisms only accomplish control of the pest.  Forestry has a great potential for utilizing biological control strategies because of the perennial nature of the system and the potential for alternative food sources.  The fact that pesticides are generally not cost-effective is another consideration. 

 
Genetic Engineering

Genetic manipulation of both the host and the pest are relatively new approaches to pest management.  Examples include the introduction of the Bt toxin into a host plant in some agricultural crops, or the release of sterile insects to prevent or reduce mating and reproduction of pest species.  More sophisticated techniques may evolve as research continues in this area.

 
Chemical Controls
 

Chemical controls include synthetic pesticides, biological pesticides and pheromones.  Most synthetic pesticides are developed for agricultural or urban use and are adapted for use in forestry.  The trend in pesticide development is for less broad-spectrum, having less impact on non-target organisms, but more toxic chemicals.  Therefore, extreme care must be taken in applying these materials.  In forestry, synthetic pesticides are generally only used on high value trees, or when attempting to eradicate and invasive pest. 

Biological pesticides are derived from plants or naturally occurring microorganisms.  Two such pesticides that are used in forestry are Bt (Bacillus thuringiensis) and Gypcheck (a baculovirus).  Bt is a specific pathogen to the caterpillars of moths and butterflies and has a short residual life span.  Gypcheck is specific to gypsy moth and also has a short residual. 

Pheromone technology is still evolving but there are examples of successful control when a pheromone was used in a mass-trapping strategy, a male-confusion strategy, or an anti-aggregating strategy.  Pheromone strategies are usually effective against low pest population levels.

 
IPM, an Example
 

Arguably the best example of IPM is the IPM toolbox for gypsy moth control.  Gypsy moth is an invasive pest that was introduced into Massachusetts in the late 1860s and has spread both west and south.  Its main impact as a tree defoliator is as a nuisance to humans at high levels, tree growth loss, and some tree mortality.  After over 100 years of research the gypsy moth IPM toolbox consists of: (1) a synthetic pheromone that is used for monitoring, mass trapping and the male confusion strategy at low population levels, (2) Bt and Gypcheck, (3) several synthetic insecticides including a growth regulator, (4) a fungus that was introduced into the North American gypsy moth environment and has spread throughout a substantial portion of the gypsy moth range, and (5) a number of parasites were introduced and have become established. These tools are currently being used in a multi-state Slow The Spread project that is design to minimize the continued spread of the gypsy moth both south and west.

Suggested Reading

Coulson, R.N. 1981. Evolution of concepts of integrated pest management in forests. J. Georgia Entomol. Soc. 16:301-316.

Coulson, R.N. and J.A. Witter. 1984. Forest Entomology Ecology and Management. Chap. 5. Concepts of Integrated Pest Management. John Wiley & Sons, New York. Pp. 97-121

Waters, W.E. and E.B. Cowling. 1976. Integrated forest pest management: A silvicultural necessity. In Apple, J.L. and R.F. Smith (Eds.), Integrated Pest Management. Plenum Press, New York.

Waters, W.E. 1978. Forest pest management: An overview and perspective. Proceedings Joint Technical Session, Convention of Society American Foresters and Canadian Institute of Forestry. St. Louis.

Waters, W. E. and R. W. Stark. 1980. Forest pest management: Concept and reality. Annu. Rev. Entomol. 25: 479-509.

Weseloh, R.M. 2003. People and the gypsy moth: a story of human interactions with an invasive species. Amer. Entomologist 49:180-190.

Posted 27 February 2008